1. Field of the Invention
The present invention relates to engine retarders of the compression release type. More particularly it relates to an improved retarder driven from a source of high pressure hydraulic fluid and triggered electronically.
2. The Prior Art
Engine retarders of the compression release type are well known in the art. In general, such retarders are designed temporarily to convert an internal combustion engine into an air compressor so as to develop a retarding horsepower which may be a substantial portion of the operating horsepower developed by the engine in its operating mode.
The basic design for an engine retarding system of the type here involved is disclosed in the Cummins U.S. Pat. No. 3,220,392. In that design an hydraulic system is employed wherein the motion of a master piston actuated by an appropriate intake, exhaust or fuel injector pushtube or rocker arm controls the motion of a slave piston which opens the exhaust valve of the internal combustion engine near the end of the compression stroke whereby the work done in compressing the intake air is not recovered during the expansion or "power" stroke but, instead, is dissipated through the exhaust and cooling systems of the engine.
A number of improvements have been made with respect to the original design shown in the Cummins U.S. Pat. No. 3,220,392. Some of these improvements were directed toward increasing the retarding horsepower developed by the mechanism while others were designed to protect components of the engine from damage.
Laas U.S. Pat. No. 3,405,699 discloses a device to unload the hydraulic system whenever excess motion of the slave piston tends to open the exhaust valve too far and hence risk damage as a result of the engine piston striking the opened exhaust valve.
Sickler et al. U.S. Pat. No. 4,271,796 discloses a pressure relief system for a compression release engine retarder wherein a bi-stable ball relief valve and damping mechanism rapidly drops the pressure in the high pressure hydraulic system to a predetermined low level whenever an excess pressure is sensed in the hydraulic system thereby obviating the risk of damage to various components of the engine valve train mechanism, particularly the pushtubes used to drive the retarder.
Price U.S. Pat. No. 4,395,884 discloses a mechanism for increasing the retarding power of a compression release retarder by increasing the flow of air through the engine during retarding. This is accomplished by diverting the exhaust to one side of the twin entry turbocharger to increase the speed of the turbocharger.
Custer U.S. Pat. No. 4,398,510 discloses an improved timing mechanism for an engine retarder which produces an increased retarding horsepower while increasing the time span between the beginning of the engine retarding action and the beginning of the normal opening of the exhaust valves of the engine.
Jakuba et al. U.S. Pat. No. 4,473,047 discloses a compression release engine retarder for an engine having dual exhaust valves wherein, during the retarding mode, only one of the dual exhaust valves is opened while in the powering mode both valves are opened.
Cavanagh U.S. Pat. No. 4,399,787 discloses an hydraulic reset mechanism particularly applicable to engine retarders of the type described in U.S. Pat. No. 4,473,047 wherein the exhaust valve opened during retarding is closed promptly after the retarding event has been completed and well before the normal opening of the dual exhaust valves begins thereby avoiding damage due to unbalanced or stress loading of the exhaust valve crosshead.
Quenneville U.S. Pat. No. 4,510,900 discloses a compression release retarder driven from a rotary pump which, in turn, is driven from the engine camshaft or crankshaft so as to bypass portions of the valve train mechanism, particularly the pushtubes.
Meistrick et al. U.S. Pat. No. 4,706,624 discloses a compression release engine retarder employing a high pressure plenum pumped by master pistons driven by the engine pushtubes. The retarder of U.S. Pat. No. 4,706,624 produces improved retarding performance by opening the exhaust valves more rapidly and at a more precisely controlled point.
Meistrick U.S. Pat. No. 4,592,319 discloses a compression release retarder in which two compression release events per cylinder are produced during each engine cycle thereby increasing the retarding horsepower developed by the engine.
Quenneville et al. U.S. Pat. No. 4,793,307 discloses an articulated rocker arm assembly for use in connection with a pushtube driven compression release retarder capable of producing two compression release events per cylinder per engine cycle. The articulated rocker arm disables the motion of the exhaust valve when the engine is in the retarding mode so as to provide for the second compression release event during each engine cycle.
In response to recent requirements that engine manufacturers reduce the emissions from the engine and increase the fuel economy, new problems have been presented affecting the engine retarder. Increased retarding power is desirable but this implies increased pushtube loading. At the same time, the clearance between the exhaust valve and the engine piston has been reduced so that the maximum opening of the exhaust valve during the compression release event is restricted. Certain of the new engines are being designed with a smaller displacement but operated at a higher speed to attain the desired operating horsepower. While increased engine speed improves the retarder performance, the time during which the retarding event is accomplished is shortened so that more precise timing and more rapid motion of the mechanism is required. Some of the new engines are being equipped with a high pressure hydraulic fluid system intended, among other things, for the operation of the fuel injectors. Such engines, not having fuel injector pushtubes, cannot be fitted with compression release retarders designed to be driven by the fuel injector pushtubes, but instead would require alternate designs such as that shown in Meistrick et al. U.S. Pat. No. Re. 33,052 and Meistrick et al. U.S. Pat. No. 4,706,624. The present invention is directed to an improved and simplified compression release retarder driven from a high pressure hydraulic fluid source rather than the engine pushtubes and designed for high performance and high speed operation to meet the needs of a new generation of engines.